1. Field of the Invention
The invention relates in general to wireless telecommunication systems, and in particular, to a method for clock calibration in a wireless telecommunication system.
2. Description of the Related Art
Wireless telecommunication systems provide voice, video, data, and signaling communication services between mobile stations, such as cellular phones, notebook computers, or personal digital assistants (PDA). The mobile stations employ portable power storage cells such as batteries, with inherently limited storage capacity, thus requiring effective power management solutions.
In one example of the power management solution, the mobile station runs at a low clock speed when inactive, referred to as power saving mode, and a high clock speed during normal mobile station operation, known as normal operation mode. FIG. 1 shows a waveform of a power consumption of a mobile phone before and during receiving paging channel data, where the x-axis represents time and y-axis represents amplitude of the power in voltage. The power consumption of the mobile phone varies with time as shown by the amplitude of the waveform. Most of the time, the mobile phone switches from a power saving mode to a normal operation mode at an idle period for receiving paging channel data, sometimes, the mode switching is caused by the request of upper level software. FIG. 1 illustrates the mobile phone initially operates at a power saving mode, and then switches to a normal operation mode for receiving paging channel data. The first peak indicates the mobile phone enters the settle time for initiating the oscillation of a high speed clock; this settle time usually lasts for 3 to 5 ms. The second peak is an interrupt indicating the mobile phone enters the normal operation mode, and power is drawn from the power supply to the microcontroller, base band and RF circuits to receive and process the data packets. When the mobile phone leaves the normal operation mode, the RF circuit is turned off, and then the high speed clock is also turned off. The power usage of a mobile station can be further reduced by decreasing the duration of the normal operation mode, or decreasing the power consumed during the normal operation mode and the power consumption due to current leakage during the power saving mode.